The present invention relates to a photomask to be used for a phase shift method and a manufacturing method for a semiconductor device using such a photomask.
When various patterns, a wiring pattern, etc., to be used for a semiconductor device are formed, for example, a method in which a phase difference is made to occur in the transmitted light through a mask is proposed as one of the methods for, improving the resolution of patterns. This type of method is generally called a phase-shift method. In such a method, disclosed in a Japanese Patent Publication No. 62-50811, for example, exposure is performed using a mask in which a transparent film for changing the phase (hereinafter referred to as a shifter) of a transmitted light is formed at least on one of the transparent portions provided on both sides of an opaque portion. According to the method, the resolution of an exposure apparatus is remarkably improved and various kinds of which are finer pattern than those obtained in conventional devices can be formed.
The phase shift method is effective when a pattern is to be formed on a mask in which adjacent transparent portions are not touching. In a case, however, where a pattern is to be formed in which a pair of adjacent transparent portions are connected to each other in a part of the pattern, a peripheral part of a shifter has to be positioned in the connecting part, so that the light intensity in the part becomes zero and the pattern of a transparent portion which is originally continuous is separated into two portions. In a Japanese Patent laid-open No. 2-078216, it is disclosed that even if there is no opaque film, minute dark spots are formed in the peripheral part of a shifter. It is difficult, however, to control the formation of minute dark spots to be generated only in a part of a peripheral part of a shifter, and a dark groove-like pattern is formed in an area corresponding to the whole peripheral part. Even if it is intended to form a pattern in a part of a peripheral part of a shifter, a thin ring-shaped groove is formed around the shifter pattern. Therefore, it is necessary to prevent the generation of such a groove, which is an unnecessary part, by some way or other.